AACC-Çalıştay-The effect of the specially designed disc milling system on the selected quality

8/3/2019 AACC-altay-The effect of the specially designed disc milling system on the selected quality

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The effect of the specially designed disc milling system on the selected qualityparameters of bulgur

Ali YILDIRIMa, Mustafa BAYRAMb, Mehmet Durdu NERb

a:Gaziantep niv.-Nizip M.Y.O., 27700-Nizip-Gaziantep [email protected]: Gaziantep niversitesi, Mh. Fak., Gda Mhendislii Blm, 27310-Gaziantep

AbstractThe effects of the specially designed disc mill at the different disc gaps (1.90, 1.60, 1.30, 1.20, 1.00, 0.80,0.60, 0.50 and 0.40 mm) on the selected quality parameters for bulgur i.e. screen analysis (g/g %), colour(L, a, b, YI), yield, loss, energy consumptions, capacity, hectolitre-weight, protein, ash, and moisturecontents were searched. The milled samples were classified as coarse (+/3.50), pilaf size (3.50/2.00),middle (2.00/1.00), fine (1.00/0.50) and by-product (0.50/-) using 3.50, 2.00, 1.00 and 0.50 mm sieves.The increase in the disc gap for the disc mill increased the percent mass of coarse products (P


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Fig. 1. Illustration of the disc mill (dimensions in millimeter)

Fig. 2. Dimensions of the top disc of the disc mill (dimensions in millimeter)

The thicknesses of disc without and with tooth were 32 and 35 mm, respectively. The centre hole of thedisc was 250 mm in diameter. The dimensions of the stationary disc were identical with the rotating one,

but there was no hole at the centre. Figs. 3 and 4 illustrated the drawing and teeth sizes of the disc mill.The alpha (sharp edge) and beta (dull edge) angles of teeth were 30o and 60o, respectively. The thicknessof teeth was 3 mm. The corrugation was designed that distances between two teeth line were 2.5 and 5mm at the inside and outside of disc, respectively (Fig. 3). The grooves on the discs were helicallyopened. The discs were worked at sharp-to-sharp position. The disc mill gap was set to 1.90, 1.60, 1.30,1.20, 1.00, 0.80, 0.60, 0.50 and 0.40 mm, giving a total of nine different samples. Screen analysis, (g/g%), moisture content (g/g %, w.b.), ash content (g/g %, d.b.), color value (L, a, b and YI), loss (g/g %),yield (g/g %) and protein content (g/g %, d.b.) of the samples were determined.


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Fig. 3. Sharp and dull angles of the teeth of the disc mill (dimensions in millimeter)

Fig. 4. Teeth size of the disc mill (dimensions inmillimeter

2.3. Sample collection and analysis

When the actual conditions were supplied i.e. 14.4 kWand 37.9 A, the disc mill was worked during further 15minutes with continuous feeding, then sample wascollected. This operation was regularly repeated at eachgap treatment. Screen analyses were carried out using

the circular sieves with 3.50, 2.00, 1.00 and 0.50 mm circular aperture made of steel. One hundred gramsample was used for the screen analysis. Moisture content (g/g %, w.b.) measured using the oven method(105oC) (AOAC, 1990). Ash contents (g/g, dry basis) were measured using the method of AOAC (1992)(for the ash content, before the measurements, all samples were screened with 2.00 mm sieve. Then,retained part of samples on this sieve was used for the ash content measurement). Bulk density (kg/hl)was measured using a graduated cylinder and analytical balance ( 0.001) (TSE, 1989). Protein contents(g/g %, d.b.) of milled samples were measured using Kjeldahl method (AOAC, 1990). Colour values (L,a, b and YI) were measured using Hunter Lab Colorimeter (Colorflex, USA). Samples were firstly

screened with 2.00 mm sieve, then retained parts were analysed for colour values. A white standard tilewas used to calibrate the colorimeter (L=93.01, a = -1.11, b = 1.30) before each measurement. L, a, b andYI-values represents lightness, redness, yellowness and yellowness index, respectively.

2.4. Determination of yield and loss

From cumulative percent mass data obtained in the screen analyses, the total quantity obtained from theupper part of 0.50 mm sieve (+/0.50 mm) and the lower part of 0.50 mm sieve (0.50mm/-) were evaluatedas the yield (g/g %, bulgur) and loss (g/g %, by-product), respectively.

2.5. Determination of energy consumption and capacity

The optimum feeding rate and capacity of the disc mill were determined by measuring ampere value.During the experiments, when the ampere reached to 37.9 Ampere i.e. optimum ampere value, thefeeding rate was fixed. Energy consumption was calculated in unit of kW (as used power)/kg (for each

product). Capacity was also determined at optimum working conditions i.e. 37.9 A, 380 V and 14.4 kW.

2.6. Statistical analysis

Data obtained was subjected to statistical analysis of variance (ANOVA) and Duncan multiple range testto assess difference between means and homogeneous subsets using the SPSS 8.0 statistical software(SPSS Inc., USA). Figures representation was carried out using the Sigma Plot 2000 (SPW 6.0, SPSSInc., USA) and Autocad 2000 Engineering Drawing Software (AutoDesk Inc., USA).

3. Results and discussion


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The milling of bulgur is different from semolina and flour milling due to cooked and dried form of wheat.Main principle during size reduction for bulgur production is the creation of new surface by dividing ofintact cooked and dried wheat kernel into two or more particles. During this operation main problems are;(i) deformation, scratching and formation of burr on the surface of bulgur particle (abrasive type mills),(ii) formation of sharp edge on granular bulgur (causes adhesiveness, breaking, flour formation andquality loss during pilaf and kfte making), (iii) loss of translucency and polish appearance of bulgur, (iv)decreasing yield due to flour formation during size reduction of disc milling, (v) loss of oval and smoothshape (formation of sharp edges), (vi) creation of different sized bulgur particles i.e. not uniform sizes(Bayram and ner, 2004c). The disc mill has many applications and is the heart of several millingsystems. It can be used with finesse to break open cereal grains such as wheat or it can be used with bruteforce to reduce granular products to fine flour. Disc mill grinds product between two discs upon whichare mounted corrugated grinding elements. Two other important factors influencing the grindcharacteristic are speed of rotation and the gap between the grinding elements. For each application thetype of corrugation, relative disposition of the corrugations (sharp to sharp, dull to dull etc.), speed andmotor size should be selected.

3.1. Screen analysis

Screen analysis for the disc milled bulgur by adjusting the disc gap to 0.40, 0.50, 0.60, 0.80, 1.00, 1.20,1.30, 1.60 and 1.90 mm was carried out using 3.50, 2.00, 1.00 and 0.50 mm screens (Table I). The coarsesize bulgur (+/3.50) was not obtained at 0.40, 0.50, 0.60 and 0.80 mm gaps due to more size reduction

effect of the teeth of the disc mill. The coarse size bulgur was obtained at 1.00 mm gap at small amounti.e. 1.29%. Increasing the gap from 1.00 to 1.90 mm significantly (P


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In the study of Bayram and ner (2004c), stone, roll and disc mills were used. In that study, the disc millused had highest by-product ratio such as 3.50%. The depth of grooves or teeth, and the gap betweendiscs were 2.50 mm that was used disc mill by Bayram and ner (2004c). The loss in the present studywould be less than that of the study of Bayram and ner (2004c) at the same disc gaps i.e. 2.50 mm. Inthat study (Bayram and ner, 2004c), the grooves were opened straight on the disc plane in contrast toopened helical shape in present study. This helical shape increased the corrugated teeth length andincreased the endurance of tooth.

3.2. Colour results

The first quality judgement made by consumers on bulgur at the point of sale and acceptability is itsvisual appearance (Bayram et al., 2004c). It is known that processing steps i.e. cooking, drying,tempering, dehulling and milling affect the colour of bulgur (Bayram et al., 2004a, 2004b, 2004c, 2004d;Bayram and ner, 2004c).

In present study, before the milling operation, the cooked and dried wheat was tempered and then branwas removed. The colour values together with some selected values i.e. protein, ash, moisture contentand hectolitre-weight were measured. The L-value i.e. lightness of cooked and dried wheat was 41.78,and then increased to 42.53 with the tempering operation. This colour value also increased to 44.76 afterthe dehulling operation. The increase in the L-value during the tempering and dehulling operations could

be due to water adsorption on the surface of the wheat kernel (water caused lightness or in another word

initial lightening) and removing dark bran using dehuller from the wheat kernel (light colour endospermunder the bran layer increased the lightness), respectively. The L-value illustrated that; the effect of thedehulling operation on lightness was greater than that of the tempering operation due to dark colour of

bran. The a-value (redness) decreased gradually during these preceding operations such as 5.04, 4.83 and4.82 for the cooked and dried, tempered and dehulled wheat, respectively. This decrease in the avaluewas correlated with the increase in the L-value.

Fig. 5. Colour values (lightness, redness, yellowness and yellowness index) of the milled samples at thedifferent disc gaps

Generally, both colour value shows opposite relation for bulgur (Bayram et al., 2004b, 2004c). Similardecreases were obtained for the b and YI-values (yellowness and yellowness index). The b-values weremeasured as 14.40, 14.21 and 16.96 for the cooked and dried, tempered and dehulled wheat, respectively.As parallel to the b-value, the YI-values was determined as 73.88, 70.54 and 68.58, respectively. The

colour values i.e. the L, a, b and YI-values of milled bulgur by using the different disc gaps, were givenin Fig. 5. The change of disc gaps were significantly (P


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gap. Also, the ash content is important for finished product quality and standards. According to TSE, ashcontent as dry basis should be less than 1.80% (TSE, 2003). This value is permitted up to 3% in USAstandards (USDA, 1996). The ash contents measured for the preceding operations i.e. the cooked anddried, tempered and dehulled wheat were 1.60, 1.57 and 1.36% (g/g, d.b), respectively. The milled bulgurat 1.90 mm gap had same ash content with dehulled wheat i.e. 1.36%. The decreasing the disc gapdecreased the ash content steadily by removing the bran content due to the abrasive effect of the tooth ofthe disc mill (P


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by shrinkage). But, for flour and semolina productions, bran is removed during milling, and there are novoid between bran and endosperm layers. In addition, in Mut type system, long tempering period isrelated with the milling operation to increase the yellow colour intensity. The inlet moisture content was13.92%. The outlet moisture contents obtained from the disc mill at different gaps were measured andgiven in Fig. 6. The increase in the gap slightly increased the outlet moisture content but all outletmoistures were less than the inlet moisture due to evaporation of water during the milling operation. Itwas observed that a small amount of heat generation during milling due to abrasive effect caused the lossof moisture. In addition, at small gap widths, the mill produced small bulgur particles i.e. high surfacearea. The level of the loss of moisture content was higher at low gaps due to high surface area creation atsmall particles and high abrasive effect (caused more heat generation).

3.7. Energy consumption and capacity

The disc mill was run by a motor (18 kW, 47.4 A) that had a speed of 970 rpm. The speed of motor wasdecreased to 250 nm at the disc using reductors. By 80% performance, the capacity of the disc mill atdifferent gaps was determined at 37.9 A and 14.4 kW (Table II). The capacity of the disc mill increasedlinearly (r2=0.958) by increasing the gap between the discs. The maximum capacity was obtained at 1.90mm such as 705 kg/h. The energy consumptions (kW/kg) were calculated dividing power by capacity ateach gap. As expected, at big gap values, the energy consumption decreased linearly (r2=0.958) due todecreasing the effects of the abrasive and size reduction effects, and friction loss. These capacities andenergy consumptions values can also be used practically in industrial base to calculate the energy

consumption and capacity for each product i.e. coarse, pilaf etc. those want to produce.

Table II: Energy consumption and capacity at different gaps

4. ConclusionsThe designed disc mill was suitable for bulgur production by arranging the disc gap. Helically openedgrooves in this study were better than previously studied the disc mill by Bayram and ner (2004c).Significant amount of pilaf, middle and fine bulgur can be produced using the disc mill presented in thisstudy by arranging the disc gap. By increasing the disc gap i.e. >1.90 mm, coarse size can also be

produced. The decreasing disc gap caused the increase in the amount of by-product and energyconsumption, and also decrease in the capacity. The ash and moisture contents decreased with decreasingthe disc gap. The increase in the disc gap for the disc mill increased the percent mass of coarse products.The coarse size bulgur was not obtained with the disc gaps of 0.40, 0.50, 0.60 and 0.80 mm.

References


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AOAC, 1990. Official methods of analysis of the association of official analytical chemists. 15th Edn.,Association of Official Analytical Chemists, Washington, DC.

Bayram, M., ner, M.D., 1996. Bulgur retiminin bugnk durumu ve sorunlar. II. Un-Bulgur-BiskviSempozyumu, Karaman-Turkey 165-177.

Bayram, M., 2000. Bulgur around the world. Cereal Foods World 45, 80-82.

Bayram, M., ner, M. D., 2002. The new old wheat: convenience and nutrition drivingdemand for bulgur, World Grain, November 51-53.

Bayram, M., ner, M.D., 2004a. 2003de bulgur sektr-1. Unlu Mamller Teknolojisi 61, 23-29.

Bayram, M., ner, M.D., 2004b. 2003de bulgur sektr-2. Unlu Mamller Teknolojisi 62, 20-30.

Bayram, M., ner, M.D., 2004c. Stone, disc and hammer milling of bulgur. Journal of Cereal Science(submitted)

Bayram, M., ner, M.D., Eren, S., 2004a. Effect of cooking time and temperature on the dimensions andcrease of the wheat kernel during bulgur production. Journal of Food Engineering 64, 43-51.

Bayram, M., Kaya, A., ner, M. D. 2004b. Changes in properties of soaking water during production ofsoy-bulgur. Journal of Food Engineering 61, 221-230.

Bayram, M., ner, M.D., Kaya, A., 2004c. Influence of soaking on the dimensions and colour of soybeanfor bulgur production. Journal of Food Engineering 61, 331-339.

Bayram, M., ner, M.D., Eren, S., 2004d. Thermodynamics of the dimensional changes in the wheatkernel during cooking for bulgur production. Food Science and Technology International 10, 243-254.

Brennan, J.G., Butters, J.R., Cowell, N.D., Lilly A.E.V., 1976. Food Engineering Operations (2nd. Ed.),National Collage of Food Technology, University of Reading, UK, 66-80.

Ercan, R., 1986. Bulgur isleme teknigi ve kimyasal bilesimi. Gda 11, 319-321.

Fisher, G.W., 1973. The technology of bulgur production. Technica-Moliteria, 24(2), 12-19.

Haley, W.L., Pence, V.M., 1960. Bulgur, an ancient wheat food. Cereal Science Today 5, 203-207,214.

Kent, N.L., 1975. Technology of cereals with special reference to wheat. 2nd Edition,Pergamon Press, London, 223.

McCabe, W.L., Smith, J.C. Harriot, P. 1985. Unit Operations of Chemical Engineering,McGraw Hill Press, NY,749-768.

ktem, R., 1984. Tarhana ve bulgur imalat teknigi gelistirme olanaklar. 9. Izmir Gda ve Tarm Fuar,

Gda Sanayiinde Teknolojik Gelismeler Sempozyumu, Ege niversitesi, Gida Mh. Bl. zmir-Turkey,115-126.

zboy, ., Kksel, H., 2002. An application of linear regression technique for predicting bulgur yieldand quality of wheat cultivars. Nahrung 46, 21-24.

Peyron, S., Surget, A., Mobille, F., Autran, J.C., Rouau, X., Abecassis, J., 2002. Relationship betweenbran mechanical properties and milling behaviour of durum wheat (Triticum Durum Desf.), Influence oftissue thickness and cell wall structure. Journal of Cereal Science 36, 377-378.


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Smith, G.S., Barta, E.J., Lazar, M.E., 1964. Bulgur production by continuous atmospheric pressureprocess. Food Technology 18, 89-92.

TSE, 1989. Tahllar-Hektolitre Arl Tayini (TS 6531). Turkish Standard Institute.

TSE, 2003. Bulgur (TS 2284). Turkish Standard Institute. USDA, 199

2D Graph 2

opening

1,901,601,301,201,000,800,600,500,40

values

0

20

40

60

80

100

120

140

%ash v.s opening

%loss v.s opening

%yield v.s opening

hectoliter v.s opening


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Disc gap (mm)

0.40 0.50 0.60 0.80 1.00 1.20 1.30 1.60 1.90

%m

ass(g/g)

0

20

40

60

80

100

Coarse bulgur(+/3.50 mm)

Pilaf bulgur (3.50/2.00 mm)

Middle bulgur (2.00/1.00 mm)

Fine bulgur (1.00/0.50 mm)

Disc Opening(mm)

1,901,601,301,201,000,800,600,500,40

%mass

0,00

20,00

40,00

60,00

80,00

100,00

/3.50mm

3.50/2.00mm2.00/1.00mm

1.00/0.50 mm


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Disc gap (mm)

0,4 0,5 0,6 0,8 1,0 1,2 1,3 1,6 1,9

%m

ass(g/g)

0

7

14

21

28

35

42

49

56

63

70

77

84

9198

(+/3.50 mm)

(3.50/2.00 mm)

(2.00/1.00 mm)

(1.00/0.50 mm)


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2D Graph 3

Opening(mm)

0,400,500,60 0,80 1,00 1,201,30 1,60 1,90

Colorvalues

0,00

20,00

40,00

60,00

80,00

100,00

L

ab

YI

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AACC-Çalıştay-The effect of the specially designed disc milling system on the selected quality